1. Field of the Invention
The present invention relates generally to the field of routing switcher networks. More particularly, the present invention relates to metropolitan area networks. Specifically, a preferred embodiment of the present invention relates to a network where at least two routing switchers are connected together with a tie-line composed of a plurality of full duplex dedicated router interconnects. This configuration results in a contention free environment as long as the number of users along a given tie-line at a given moment does not exceed the number of dedicated routing switcher interconnects that compose that tie-line. The present invention thus relates to a metropolitan area network of the type that can be termed almost contention free (i.e., nearly latency free).
2. Discussion of the Related Art
Within this application two publications are referenced by superscripts composed of arabic numerals within brackets. Full citations for both of these publications may be found at the end of the specification immediately preceding the claims. The disclosures of both of these publications in their entireties are hereby expressly incorporated by reference into the present application for the purposes of indicating the background of the present invention and illustrating the state of the art.
Historically, it was known in the prior art to connect routing switchers together in networks..sup.[1] Such networks are referred to as local area networks (LANs), metropolitan area networks (MANs), or wide area networks (WANs), depending on their geographic extent. WANs generally extend over distances greater than approximately 150 Km. MANs generally extend over distances of from approximately 2 Km to approximately 150 Km. LANs generally extend over distances less than approximately 2 Km.
As is known to those skilled in the art, routing switchers can be connected together with tie-lines in order to assemble a network. Prior art routing switchers sometimes called routers, are well-known to those skilled in the art. A conventional routing switcher is typically a cross bar switch which can be represented as a matrix having a size of from (2).times.(2) to (128).times.(128), or even larger. For example, a (4).times.(4) cross bar switch permits an incoming signal on one of four different incoming interconnects to be routed to any one of, any two of, any three of, or all of the four different outgoing interconnects. The cross bar feature permits the signal to be routed to any combination of the outgoing interconnects, without any mutual exclusivity. The interconnects themselves can be ordinary twisted pair, optical fiber, or even a free-space radio connection such as, for example, a microwave link.
As is also known to those of skill in the art, time sensitive data must be transferred with laminarity to avoid distortion. For example, if a real-time video signal is transferred intermittently, the received image will appear jittery. Similarly, real-time audio must be transferred with laminarity to avoid distortion. Thus, there is a need for real-time multi-media data to be transferred with laminarity. Such real-time data can be termed continuous data.
As is also known to those of skill in the art, the operation of networks that transfer continuous data has in the past been inefficient. This is because the control information that is used to configure and reconfigure the routing switchers is intermittent (i.e., bursty). In more detail, such control data only needs to be transferred when a configuration, or reconfiguration, of the network is required. Typically, such a requirement is instigated by one or more users who desire to establish a new connection through the network, for example, when a new user desires to join a multi-media conference that is already in progress.
Thus, a problem has been that the control information cannot be transmitted between routing switchers on interconnects that are being used by the network to transfer time sensitive user data such as, for example, the real-time video and/or real-time audio that composes a multi-media conference. Where such time sensitive data must be transferred, asynchronous transfer mode (ATM) is of no use because the packetization that is inherent to the ATM technique disrupts the laminarity of the time sensitive data.
One unsatisfactory approach, in an attempt to solve the problems referred to above, involves providing a parallel control network between the routing switchers in a network. However, a major disadvantage of using such a parallel control network is all the attendant costs of the parallel control network (e.g., control tie-lines, control routers and control terminals) that must be incurred. Another disadvantage of using such a parallel control network is the users themselves cannot directly reconfigure the routing switchers unless every user site is provided with a parallel control terminal. Instead, the users must typically request that a reconfiguration be carried out by the parallel control network. Some parallel control networks even require a human operator to be telephoned and requested to manually input the reconfiguration information. This type of situation can lead to lengthy delays when an operator is not available, or is otherwise busy, at the time a user wants to affect a configuration or reconfiguration.
Another unsatisfactory approach involves dedicating some of the interconnects to control data duty. However, a disadvantage of dedicating some of the interconnects to control data duty is that a fraction of the interconnects are consequently unavailable for user data transfer. This can be a significant drawback when the number of users desiring to use a particular tie-line exceeds the number of interconnects available for user data transfer through that particular tie-line (i.e., contention). Another disadvantage of dedicating some of the interconnects to control data duty is that the control interconnects themselves are often idle. Control information is often not needed for long periods, particularly when the number of users is relatively constant. So dedicating interconnects to control data duty, particularly where a large fraction of the interconnects must be so dedicated, is a tremendous waste of bandwidth.